In most cases, damage along the trellis will diminish with distance because
metal posts and/or trees attached to the trellis will act as grounds to
dissipate the charge. How many trees are killed or damaged will depend on many
different factors, including the strength of the initial lightening strike, the
size and moisture content of the trees that are tied to the wire, and the
conductivity of trellis posts. Pressure-treated wooden line posts may serve to
direct the current to the ground when the posts are wet from rain, so in some
cases only a single “panel” of trees will be killed or severely damaged.
Most growers overlook lightening as a cause of sudden tree death during summer.
I’ve been called out to diagnose tree deaths caused by lightening at least six
times over the past 35 years. Usually the grower will “This tree was perfect
last time I sprayed and now it is dead!” Things that assist in diagnosing
lightening include the following:
1. The killed trees or dead limbs appear very suddenly, often in
mid-summer (because that is when we get most of our thunderstorms). Brown-black
leaves are still attached to the dead trees or limbs. The killed leaves may
have sharply bent petioles, presumably because the rapid desiccation caused by
the heating deforms the normal arc of the leaf petiole.
2. On trees that are not attached to a trellis, one or two trees at the
center of the strike may be completely killed, but the tallest twigs or limbs
on adjacent trees may show dieback caused by parallel charges that are of lower
intensity than the main charge. The lesser charges that kill shoot tips in
adjacent trees dissipates to sub-lethal levels as it moves into heavier wood,
thereby killing only is the smaller and most exposed shoots.
3. Tangential cuts through recently killed terminal shoots may show
“pelletized” pith in the center of the shoots because the pith contains more
water than other shoot tissue and therefore shrinks into distinct segments or
“pellets” when it is instantaneously desiccated from heat associated with the
electrical charge.
4. Several weeks after the damage was incurred, tangential cuts made
through 1-in diameter limbs that still have normal leaves but that are located
below killed sections of limbs will often reveal a ring of brown/black xylem
tissue just inside the bark. The ring occurs when some of the youngest
(outermost) xylem tissue is killed by the electrical charge but the cambium
survives and generates healthy new xylem that overlays the damaged xylem.
5. In southeastern New York, trunks of trees killed by lightening are
often covered by fungal bracts within several weeks after the lightening strike
occurred. These bract fungi can sporulate very quickly on the killed trees
because they were already present in the discolored xylem that is often evident
in cross-sections of older trees. The tree’s natural defenses keeps these
xylem-invading fungi from moving outward into younger xylem, but they can only
sporulate if xylem is killed all the way to the bark surfaces. When lightening
kills a tree, the killed wood and the water it contains provides the perfect
food sources for the bract fungi, so they rapid invade the wood and bark and
produce bracts.
****************************************************************
Dave Rosenberger, Professor Emeritus
Dept. of Plant Pathology and Plant-Microbe Biology
Cornell’s Hudson Valley Lab, P.O. Box 727, Highland, NY 12528
Office: 845-691-7231 Cell: 845-594-3060
http://blogs.cornell.edu/plantpathhvl/blog-2014/
****************************************************************
On Jan 13, 2015, at 12:17 PM, Rob Crassweller
<r...@psu.edu<mailto:r...@psu.edu>> wrote:
Lightning can indeed strike the new high density system wires. The charge will
travel down the wire and literally "fry" the trees killing them. How many it
kills will depend on the strength of the strike and how long your rows are.
Rob Crassweller
Professor of Horticulture
Penn State University
r...@psu.edu<mailto:r...@psu.edu>
Sent from my iPad
On Jan 13, 2015, at 11:56 AM, Steven Bibula
<sbib...@maine.rr.com<mailto:sbib...@maine.rr.com>> wrote:
Anyone know of lightning strikes on wire trellised systems, and the effects on
the trees?
Has anyone studied the attractiveness of these systems to lightning strikes,
and whether grounding and foliage has much to do with it?
Steven Bibula
Plowshares Community Farm
Gorham ME
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